If you grow your own herbs you probably use small amounts all season long. But you can also easily dry some – or take advantage of the seasonal bounty at your local store or farmer's market – for a year-round supply of high quality herbs.

Air drying is the easiest, most inexpensive method for preserving herbs. Moisture evaporates slowly and naturally during air drying, leaving the flavorful essential oils behind. Sturdy herbs such as sage, thyme, summer savory, dill, bay leaves, oregano, rosemary and marjoram are well suited for air-drying. 

Tender-leafed herbs such as basil, tarragon, lemon balm and the mints have a high moisture content and will mold if not dried quickly, so these are not as suitable for air drying. A dehydrator is best for drying these high moisture herbs. A microwave oven can be used as a last resort for drying, but the microwaves literally cook the herbs, producing very poor quality.

The best time to harvest most herbs for drying is just as the flower buds first appear. The leaves contain the most oil at this growth stage, so the finished product will have the greatest flavor and fragrance. But they can still be harvested and dried after they have already flowered. Many annual and perennial herbs can be harvested in midsummer and again in the fall.

Remove approximately 1/3 of the current year's growth on perennial herbs. Annual herbs can be cut back more severely, and these can be cut down to the ground when harvesting just before the first frost. Stop making large harvests of the perennial herbs in late summer or fall to allow the new growth to harden before winter. However, small harvests can be made during most of the fall. Sage flavor may actually be improved by two or three frosts prior to harvest.

Harvest herbs in mid-morning when the leaves are dry, but before the sun is hot. Use garden shears, scissors or a sharp knife to cut large stems or branches from the plants.  Gently shake the branches to remove any insects or debris, but be careful not to bruise the leaves. Remove any old, damaged or diseased leaves and any blossoms. Rinse the branches in cool water and gently shake to remove excess moisture. Dry with towels or paper towels to remove all visible water. Wet herbs can mold, which will destroy the whole bunch.

The easiest way to air dry sturdy herbs is to tie the washed branches into small bundles (5-6 stems) and hang them upside down, in a warm (70-80°F), dry, well-ventilated area out of direct sunlight. Finding the right spot is sometimes difficult: basements are usually too damp; garages have car fumes. Attics or linen closets are often a good choice. Just make sure there is good air circulation so the herbs don't get moldy.

Let them hang until the moisture evaporates (generally 2-4 weeks). Herbs can be air-dried outdoors, but better color and flavor retention usually results from drying indoors (especially in the humid Midwest). The bunches can be placed in a paper bag, with holes cut in the sides for air circulation, to protect them from dust the bag and to catch any leaves or seeds that fall off. Gather the bag around the stems and tie. Make sure there is plenty of room inside the bag so leaves do not touch the sides of the bag. 

Another way to air dry herbs is to place them on a drying tray. A simple drying tray consists of fine mesh screen or cheesecloth attached to a wooden frame. A small window screen also works well. Place blocks under the corners of the drying tray to insure good air circulation. Place a single layer of leaves or branches on the drying surface and keep the herbs in a warm, dry area until they are thoroughly dry. This is a good way to dry chopped chives.

To dry herb seeds, such as dill, caraway and coriander, harvest the seedheads just before they turn brown so that the seeds don't fall off while cutting. Cut off the entire head and place in a paper bag. Then place the bags in a warm, dry area. Seeds generally take longer than leaves to dry. After drying, shake the seeds loose into the bag and remove any chaff.

The moister herbs can sometimes be air dried as for sturdy herbs, but this is most successful when relative humidity is low. Tie the stems in smaller bunches and check these bunches periodically for mold and discard any diseased bunches.

A gas or electric oven can also be used to dry herbs. Spread a layer of leaves or stems on a cookie sheet or shallow baking pan and place the herbs in a warm (up to 180°F) oven for 3 to 4 hours. Leave the door open and stir the herbs periodically until they are thoroughly dry. The cool oven method dries the leaves separately. The best leaves are removed from the stems and arranged on a paper towel without touching. This layer is covered with another towel and another layer of leaves is added. Five layers may be dried at one time using this method. Dry in a very cool oven. The oven light of an electric range or the pilot light of a gas range furnishes enough heat for overnight drying. Leaves dry flat and retain a good color.

A microwave oven can be used for small quantities of herbs. Place 4 or 5 herb branches in the oven between paper towels. Heat for two to three minutes on high. If not brittle and dry when removed from the oven, repeat microwave drying for 30 seconds more. The heat generated during microwaving not only removes moisture, but some of the oils, so these herbs may not have as intense a flavor as herbs dried by other methods.

When the leaves are dry, strip the leaves from stems, discarding the stems. You can crush the leaves if you want, but whole herbs retain their flavor longer than crushed, ground or rubbed herbs.

Place dried herbs in airtight containers, such as zip closure plastic bags, canning jars, or tightly sealed plastic containers. Examine the containers for a couple of days after filling to make sure they are completely dry. If you see any moisture in the containers, remove the herbs and dry them longer. Store in a cool, dry, dark place away from sunlight to protect the color and fragrance of the dried herbs. Dried herbs will keep for years, but for best flavor use within a year. Most herbs will diminish in flavor with age and a larger amount will be needed to achieve the desired flavor in cooking. Sage is the only herb that will grow stronger in flavor during storage. 

– Susan Mahr, University of Wisconsin